• Structural Engineering and Mechanics
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• 제60권4호
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• pp.633-653
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• 2016

One of the major threats to the stability of classical columns and colonnades are earthquakes. The behavior of columns under high seismic excitation loads is non-linear and complex since rocking, wobbling and sliding failure modes can occur. Therefore, three dimensional simulation approaches are essential to investigate the in-plane and out-of-plane response of such structures during harmonic and seismic loading excitations. Using a software based on the Distinct Element Method (DEM) of analysis, a three dimensional numerical study has been performed to investigate the parameters affecting the seismic behaviour of colonnades' structural systems. A typical section of the two-storey colonnade of the Forum in Pompeii has been modelled and studied parametrically, in order to identify the main factors affecting the stability and to improve our understanding of the earthquake behaviour of such structures. The model is then used to compare the results between 2D and 3D simulations emphasizing the different response for the selected earthquake records. From the results analysis, it was found that the high-frequency motion requires large base acceleration amplitude to lead to the collapse of the colonnade in a shear-slip mode between the drums. However, low-frequency harmonic excitations are more prominent to cause structural collapse of the two-storey colonnade than the high-frequency ones with predominant rocking failure mode. Finally, the 2D analysis found to be unconservative since underestimates the displacement demands of the colonnade system when compared with the 3D analysis.

• 마이크로전자및패키징학회지
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• 제12권4호통권37호
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• pp.331-338
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• 2005

The rapid advances in high power light sources and arrays as encountered in incandescent lamps have induced dramatic increases in die heat flux and power consumption at all levels of high power LED packaging. The lifetime of such devices and device arrays is determined by their temperature and thermal transients controlled by the powering and cooling, because they are usually operated under rough environmental conditions. The reliability of packaged electronics strongly depends on the die attach quality, because any void or a small delamination may cause instant temperature increase in the die, leading sooner or later to failure in the operation. Die attach materials have a key role in the thermal management of high power LED packages by providing the low thermal resistance between the heat generating LED chips and the heat dissipating heat slug. In this paper, thermal transient characteristics of die attach in high power LED package have been studied based on the thermal transient analysis using the evaluation of the structure function of the heat flow path. With high power LED packages fabricated by die attach materials such as Ag paste, solder paste and Au/Sn eutectic bonding, we have demonstrated characteristics such as cross-section analysis, shear test and visual inspection after shear test of die attach and how to detect die attach failures and to measure thermal resistance values of die attach in high power LED package. From the structure function oi the thermal transient characteristics, we could know the result that die attach quality of Au/Sn eutectic bonding presented the thermal resistance of about 3.5K/W. It was much better than those of Ag paste and solder paste presented the thermal resistance of about 11.5${\~}$14.2K/W and 4.4${\~}$4.6K/W, respectively.

• 터널과지하공간
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• 제30권4호
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• pp.404-416
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• 2020

2차원 응력조건에서 V형 암석노치의 파괴하중을 계산하는 해석적 절차를 slip-line 소성해석법 기반으로 개발하였다. 노치 주변의 암석이 소성상태에 있을 때 slip-line 중 하나인 α선이 암석 노치 면과 노치 외부 수평면을 연결한다는 사실과 α선을 따라서 변하지 않는 불변량이 존재한다는 이론적 사실이 해석적 절차 개발과정에서 핵심 아이디어로 활용되었다. 암석 노치 외부 수평면의 응력 경계조건을 알고 있으므로 불변량 방정식을 풀면 암석 노치 면에 작용하는 수직응력과 전단응력을 계산하는 것이 가능해진다. 노치 면에 작용하는 응력성분 값을 이용하여 쐐기에 의해 노치에 가해지는 파괴하중을 계산하였다. 개발된 해석적 절차를 적용하여 암석 노치파괴 해석을 수행하였다. 암석 노치의 파괴하중은 노치의 각도 및 노치 면의 마찰이 증가함에 따라 지수함수적 비선형성을 가지고 증가하는 특성이 있음을 해석결과는 보여주었다. 이 연구에서 개발한 해석적 절차는 쐐기형 노치 형성을 통한 암석균열 개시조건 연구, 암반 기초 지지력 계산, 암반사면 및 원형터널의 안전성 해석 등에 응용될 수 있을 것으로 기대된다.

• International Journal of Aeronautical and Space Sciences
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• 제12권2호
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• pp.115-133
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• 2011

Fiber reinforced polymer composites (FRPs) are being increasingly used for a wide range of engineering applications owing to their high specific strength and stiffness. However, their through-the-thickness performance lacks some of the most demanding physical and mechanical property requirements for structural applications, such as aerospace vehicles and military components. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs), due to their excellent mechanical, thermal and electrical properties, offer great promise to improve the weak properties in the thickness direction and impart multi-functionality without substantial weight addition to FRPs. This paper reviews the progress made to date on i) the techniques developed for integration of CNTs/ CNFs into FRPs, and ii) the effects of the addition of these nanofillers on the interlaminar properties, such as such interlaminar shear strength, interlaminar fracture toughness and impact damage resistance and tolerance, of FRPs. The key challenges and future prospects in the development of multiscale CNT-FRP composites for advanced applications are also highlighted.

• 한국화재소방학회논문지
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• 제23권4호
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• pp.59-66
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• 2009

본 연구는 합성구조에 사용되는 스터드커넥터의 화재시 성능에 대한 연구이다. 스터드커넥터는 전단연결재로 가장 폭넓게 사용되고 있으며, 콘크리트와 강재를 일체화시켜 합성 성능을 확보한다. 스터드커넥터에 대한 상세 내화성능은 아직 명확한 자료가 없으며, 향후 성능설계에서 무피복 합성보 등에 대한 설계 자료로 요구 된다. 본 실험의 스터드커넥터 성능시험은 푸시 아웃 실험을 변형하여 특수 전기로와 결합 ISO 표준온도곡선을 기본으로 거동 성능실험을 수행하였으며, 화재 조건의 파괴 형상을 기반으로 성능 분석 방법을 제안하였다.

• Computers and Concrete
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• 제32권3호
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• pp.339-349
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• 2023

Fast-built construction is a key feature for successful applications of precast concrete (PC) moment frame system in recent construction practices. To this end, by introducing some unique splicing details in precast connections, especially between PC columns including panel zones, use of temporary supports and bracings can be minimized based on their self-sustaining nature. In addition, precast wide beams are commonly adopted for better economic feasibility. In this study, three self-sustaining precast concrete (PC) wide beam-column connection specimens were fabricated and tested under reversed cyclic loadings, and their seismic performances were quantitatively evaluated in terms of strength, ductility, failure modes, energy dissipation and stiffness degradation. Test results were compared with ASCE 41-17 nonlinear modeling curves and its corresponding acceptance criteria. On this basis, an improved macro modeling method was explored for a more accurate simulation. It appeared that all the test specimens fully satisfy the acceptance criteria, but the implicit joint model recommended in ASCE 41-17 tends to underestimate the joint shear stiffness of PC wide beam-column connection. While, the explicit joint model along with concentrated plastic hinge modeling technique is able to present better accuracy in simulating the cyclic responses of PC wide beam-column connections.

• Structural Engineering and Mechanics
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• 제75권3호
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• pp.401-414
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• 2020

Unlike the existing truss models for shear and torsion analysis, in this study, the torsional capacities of reinforced concrete (RC) members were estimated by introducing multi-potential capacity criteria that considered the aggregate interlock, concrete crushing, and spalling of concrete cover. The smeared truss model based on the fixed-angle theory was utilized to obtain the torsional behavior of reinforced concrete member, and the multi-potential capacity criteria were then applied to draw the capacity of the member. In addition, to avoid any iterative calculation in the existing torsional behavior model, a simple strength model was suggested that considers key variables, such as the effective thickness of torsional member, principal stress angle, and strain effect that reduces the resistance of concrete due to large longitudinal tensile strain. The proposed multi-potential capacity concept and the simple strength model were verified by comparing with test results collected from the literature. The study found that the multi-potential capacity could estimate in a rational manner not only the torsional strength but also the failure mode of RC members subjected to torsional moment, by reflecting the reinforcing index in both transverse and longitudinal directions, as well as the sectional and material properties of RC members.

• 한국전산구조공학회논문집
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• 제22권2호
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• pp.181-187
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• 2009

내진 설계기준이 도입된 이후, 신설교량에 대한 내진 설계의 시행은 물론 기존교량의 내진 성능 검토에 의한 내진 성능 확보가 요구되고 있다. 기존교량의 내진 성능 확보 또한 내진 설계의 기본개념에 따라 붕괴방지수준을 만족하여야 하며, 확보방안으로는 교량의 중요도와 형식에 따라 보강규모가 다른 여러 가지 방안이 제시되어야 한다. 현재 일반교량의 경우 받침의 교체, 교각의 보강 및 전단키 설치 등의 보강방안이 내진 성능 향상 및 확보 방안으로 가장 많이 연구, 적용되고 있는 상황이다. 이 연구에서는 내진 설계가 수행되지 않은 일반적인 기존 교량은 해석대상교량으로 선정하고, 붕괴방지 수준을 만족하기 위해 연성파괴메카니즘을 확보하도록 기존교량의 설계변경을 수행하고 내진 성능을 검토하였다. 기존교량의 경우, 하부구조 교각기둥의 설계단면 결정 및 상/하부구조 연결부 받침의 기능변경 등 교량시스템의 재 설계에 의해 내진 성능을 확보할 수 있다는 것을 제시하였다.

• Steel and Composite Structures
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• 제49권4호
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• pp.381-392
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• 2023

This study experimentally investigates the flexural behavior of steel-UHPC composite slabs composed of an innovative negative Poisson's ratio (NPR) steel plate and Ultra High Performance Concrete (UHPC) slab connected via demountable high-strength bolt shear connectors. Eight demountable composite slab specimens were fabricated and tested under traditional four-point bending method. The effects of loading histories (positive and negative bending moment), types of steel plate (NPR steel plate and Q355 steel plate) and spacings of high-strength bolts (150 mm, 200 mm and 250 mm) on the flexural behavior of demountable composite slab, including failure mode, load-deflection curve, interface relative slip, crack width and sectional strain distribution, were evaluated. The results revealed that under positive bending moment, the failure mode of composite slabs employing NPR steel plate was distinct from that with Q355 steel plate, which exhibited that part of high-strength bolts was cut off, part of pre-embedded padded extension nuts was pulled out, and UHPC collapsed due to instantaneous instability and etc. Besides, under the same spacing of high-strength bolts, NPR steel plate availably delayed and restrained the relative slip between steel plate and UHPC plate, thus significantly enhanced the cooperative deformation capacity, flexural stiffness and load capacity for composite slabs further. While under negative bending moment, NPR steel plate effectively improved the flexural capacity and deformation characteristics of composite slabs, but it has no obvious effect on the initial flexural stiffness of composite slabs. Meanwhile, the excellent crack-width control ability for UHPC endowed composite members with better durability. Furthermore, according to the sectional strain distribution analysis, due to the negative Poisson's ratio effect and high yield strength of NPR steel plate, the tensile strain between NPR steel plate and UHPC layer held strain compatibility during the whole loading process, and the magnitude of upward movement for sectional plastic neutral axis could be ignored with the increase of positive bending moment.

• Geomechanics and Engineering
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• 제12권3호
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.